Dr. Tatiana DA ROS
Ramsay, A.; Fliniaux, O.; Quéro, A.; Molinié, R.; Demailly, H.; Hano, C.; Paetz, C.; Roscher, A.; Grand, E.; Kovensky, J.; Schneider, B.; Mesnard, F.
The main flax lignan, secoisolariciresinol diglucoside, is stored in a macromolecule containing other ester-bound phenolic compounds. In this study, NMR and HPLC-UV analyses were performed on flaxseeds harvested at different developmental stages to identify and quantify the main phenolic compounds produced during seed development. Extraction was carried out with or without alkaline hydrolysis to determine if these molecules accumulate in the lignan macromolecule and/or in a free form. Monolignol glucosides accumulate in a free form up to 9.85 mg/g dry matter at the early developmental stages. Hydroxycinnamic acid glucosides and flavonoid accumulate (up to 3.18 and 4.07 mg/g dry matter, respectively) in the later developmental stages and are ester-bound in the lignan macromolecule. Secosiolariciresinol diglucoside accumulates (up to 28.65 mg/g dry matter) in the later developmental stages in both forms, mainly ester-bound in the lignan macromolecule and slightly in a free form.
Lu, H.; Drelich, A.; Omri, M.; Pezron, I.; Wadouachi, A.; Pourceau, G.
Large quantities (>3 g) of a new series of alkyl uronates were synthesized in two steps from commercial methyl hexopyranosides. Firstly, several tens of grams of free methyl α-d-glucopyranoside were selectively and quantitatively oxidized into corresponding sodium uronate using 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO)-catalyzed oxidation. Hydrophobic chains of different length were then introduced by acid-mediated esterification with fatty alcohols (ethyl to lauryl alcohol) leading to the desired alkyl glucuronates with moderate to good yields (49%–72%). The methodology was successfully applied to methyl α-d-mannopyranoside and methyl β-d-galactopyranoside. Physicochemical properties, such as critical micelle concentration (CMC), equilibrium surface tension at CMC (γcmc), solubility, and Krafft temperature were measured, and the effect of structural modifications on surface active properties and micelle formation was discussed.
Flasque, M.; Nhien, A. N. V.; Moia, D.; Barnes, P. R. F.; Sauvage, F.
Solid electrolyte interphase (SEI) layers form on sensitized-TiO2 photoanodes and platinum counter electrodes when dye-sensitized solar cells (DSSCs) are subjected to an accelerated aging protocol (e.g., heating at 85 °C in the dark for 500 h). To understand how this impacts device operation, we conducted an electrochemical impedance spectroscopy study and found that the SEI induces an additional electron-transfer process from the TiO2 to the electrolyte. This is materialized by the onset of a new charge-transfer semicircle at higher frequencies, predominantly visible under bias voltages similar to and greater than the open-circuit voltage. Our results emphasize the detrimental role of SEI formation on device performance and lifetime. Additionally, nanosecond transient absorption spectroscopy showed that SEI formation reduced the rate of oxidized dye regeneration. We also found that a proportion of the photogenerated holes on the dyes were transferred to the SEI itself. A prolonged aging duration led to the electrode’s mesoporosity network being entirely clogged by the SEI, thus impeding efficient transport of the electrolyte redox couple and being responsible for a further decline in photovoltaic performances.
Bacterial lectins are nonenzymic sugar-binding proteins involved in the formation of biofilms and the onset of virulence. The weakness of individual sugar-lectin interactions is compensated by the potentially large no. of simultaneous copies of such contacts, resulting in high overall sugar-lectin affinities and marked specificities. Therapeutic compds. functionalized with sugar residues can compete with the host glycans for binding to lectins only if they are able to take advantage of this multivalent binding mechanism. Glycopeptide dendrimers, featuring treelike topologies with sugar moieties at their leaves, have already shown great promise in this regard. However, optimizing the dendrimers' amino acid sequence is necessary to match the dynamics of the lectin active sites with that of the multivalent ligands. This work combines long-time-scale coarse-grained simulations of dendrimers and lectins with a reasoned exploration of the dendrimer sequence space in an attempt to suggest sequences that could maximize multivalent binding to the galactose-specific bacterial lectin LecA. These candidates are validated by simulations of mixed dendrimer/lectin solns., and the effects of the dendrimers on lectin dynamics are discussed. This approach is an attractive first step in the conception of therapeutic compds. based on the dendrimer scaffold and contributes to the understanding of the various classes of multivalency that underpin the ubiquitous "sugar code".
Laclef, S.; Toumieux, S.; Kovensky, J.
Carbohydrates and their analogs are key molecules with a wide range of biological activities. These bioactive compounds are usually synthesized through derivatization of naturally occurring carbohydrates. Nevertheless, this strategy suffers from a limited range of naturally available monosaccharide building blocks and the necessity of laborious steps of protection and deprotection. Consequently new methods began to emerge and Diels-Alder reaction appeared to be a method of choice for their de novo production. The synthesis of carbohydrates and their analogs by means of cycloaddition reactions will be reviewed here. Moreover the potentiality of the use of monosaccharides to induce chirality in Diels-Alder reaction will be presented. Efficient methods for the synthesis of di- and tri-saccharides using the developments shown previously will be also introduced.